Deferring data record changes using query rewriting

ABSTRACT

Staging data record changes from a faster storage medium to a slower storage medium using data query rewriting is provided. In response to receiving a data query corresponding to a particular data record, it is determined whether the data query is one of a transactional data query or an analytical data query. In response to determining that the data query is a transactional data query, the transactional data query is rewritten to apply transactional delta changes to the particular data record on a storage-class memory of a computer. In response to determining that the data query is an analytical data query, the analytical data query is rewritten to select and reconcile each data record corresponding to the particular data record stored on the storage-class memory with the particular data record stored on a persistent data storage device of the computer.

BACKGROUND 1. Field

The disclosure relates generally to querying data records and morespecifically to rewriting data queries to defer data record changesusing a fast data storage medium.

2. Description of the Related Art

Supporting analytical-type data queries in conjunction with onlinetransaction processing (OLTP) workloads that are update-intensive havehistorically been problematic. One possible approach is to reduce thenumber of indexes when faced with update-intensive online transactionprocessing workloads. However, this approach makes it more difficult toefficiently process analytical-type data queries and to locate datarecords based on secondary attributes. These capabilities of efficientlyprocessing analytical-type data queries and locating data records basedon secondary attributes are often important for operational data stores.For example, it is not uncommon to find tens of indexes to improveanalytical and decision-making data queries.

SUMMARY

According to one illustrative embodiment, a computer-implemented methodfor staging data record changes from a faster storage medium to a slowerstorage medium using data query rewriting is provided. In response to acomputer receiving a data query corresponding to a particular datarecord, the computer determines whether the data query is one of atransactional data query or an analytical data query. In response to thecomputer determining that the data query is a transactional data query,the computer rewrites the transactional data query to applytransactional delta changes to the particular data record on astorage-class memory of the computer. In response to the computerdetermining that the data query is an analytical data query, thecomputer rewrites the analytical data query to select and reconcile eachdata record corresponding to the particular data record stored on thestorage-class memory with the particular data record stored on apersistent data storage device of the computer. According to otherillustrative embodiments, a computer system and a computer programproduct for staging data record changes from a faster storage medium toa slower storage medium using data query rewriting also are provided.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram of a data processing system in which illustrativeembodiments may be implemented;

FIG. 2 is a diagram illustrating deferred data record updates usingquery rewriting in accordance with an illustrative embodiment;

FIG. 3 is a diagram illustrating an example of reconciling data recordsduring a select data query operation in accordance with an illustrativeembodiment;

FIG. 4 is a diagram illustrating an example of reconciling data recordsduring an insert data query operation in accordance with an illustrativeembodiment;

FIG. 5 is a diagram illustrating an example of reconciling data recordsduring a delete data query operation in accordance with an illustrativeembodiment;

FIG. 6 is a diagram illustrating an example of reconciling data recordsduring an update data query operation in accordance with an illustrativeembodiment;

FIG. 7 is a flowchart illustrating a process for generating a databaseto store data records in accordance with an illustrative embodiment;

FIG. 8 is a flowchart illustrating a process for rewriting data queriesin accordance with an illustrative embodiment;

FIG. 9 is a flowchart illustrating a process for querying a database inaccordance with an illustrative embodiment;

FIG. 10 is a flowchart illustrating a process for performing a selectdata query in accordance with an illustrative embodiment;

FIG. 11 is a flowchart illustrating a process for performing an insertdata query in accordance with an illustrative embodiment;

FIG. 12 is a flowchart illustrating a process for performing an updatedata query in accordance with an illustrative embodiment; and

FIG. 13 is a flowchart illustrating a process for performing a deletedata query in accordance with an illustrative embodiment.

DETAILED DESCRIPTION

As will be appreciated by one skilled in the art, aspects of theillustrative embodiments may be embodied as a computer system,computer-implemented method, or computer program product. Accordingly,aspects of the illustrative embodiments may take the form of an entirelyhardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.), or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module,” or “system.” Furthermore,aspects of the illustrative embodiments may take the form of a computerprogram product embodied in one or more computer readable medium(s)having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, or semiconductor system, apparatus, or device, or anysuitable combination of the foregoing. More specific examples (anon-exhaustive list) of the computer readable storage medium wouldinclude the following: a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), a portablecompact disc read-only memory (CD-ROM), an optical storage device, amagnetic storage device, or any suitable combination of the foregoing.In the context of this document, a computer readable storage medium maybe any tangible medium that can store a program for use by or inconnection with an instruction execution system, apparatus, or device.In addition, a computer readable storage medium does not include apropagation medium, such as a signal or carrier wave.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, infra-red, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of theillustrative embodiments may be written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Java, Smalltalk, C++ or the like and conventionalprocedural programming languages, such as the “C” programming languageor similar programming languages. The program code may execute entirelyon the user's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the illustrative embodiments are described below withreference to flowchart illustrations and/or block diagrams ofcomputer-implemented methods, computer systems, and computer programproducts according to illustrative embodiments. It will be understoodthat each block of the flowchart illustrations and/or block diagrams,and combinations of blocks in the flowchart illustrations and/or blockdiagrams, can be implemented by computer program instructions. Thesecomputer program instructions may be provided to a processor of ageneral purpose computer, special purpose computer, or otherprogrammable data processing apparatus to produce a machine, such thatthe instructions, which execute via the processor of the computer orother programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

These computer program instructions may also be stored in a computerreadable storage medium that can direct a computer, other programmabledata processing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablestorage medium produce an article of manufacture including instructionswhich implement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

With reference now to the figures, and in particular, with reference toFIGS. 1 and 2, diagrams of data processing environments are provided inwhich illustrative embodiments may be implemented. It should beappreciated that FIGS. 1 and 2 are only meant as examples and are notintended to assert or imply any limitation with regard to theenvironments in which different embodiments may be implemented. Manymodifications to the depicted environments may be made.

FIG. 1 depicts a diagram of a data processing system in accordance withan illustrative embodiment. Data processing system 100 is an example ofa computer device in which computer readable program code orinstructions implementing processes of illustrative embodiments may belocated. Data processing system 100 may be, for example, a servercomputer or a client computer connected to a network, such as a localarea network, a wide area network, an intranet, an internet, or theInternet. In this illustrative example, data processing system 100includes communications fabric 102, which provides communicationsbetween processor unit 104, memory 106, storage-class memory (SCM) 108,persistent storage 110, communications unit 112, input/output (I/O) unit114, and display 116.

Processor unit 104 serves to execute instructions for softwareapplications or programs that may be loaded into memory 106. Processorunit 104 may be a set of one or more processors or may be amulti-processor core, depending on the particular implementation.Further, processor unit 104 may be implemented using one or moreheterogeneous processor systems, in which a main processor is presentwith secondary processors on a single chip. As another illustrativeexample, processor unit 104 may be a symmetric multi-processor systemcontaining multiple processors of the same type.

Memory 106, storage-class memory 108, and persistent storage 110 areexamples of computer readable storage devices 118. A computer readablestorage device is any piece of hardware that is capable of storinginformation, such as, for example, without limitation, data, computerreadable program code in functional form, and/or other suitableinformation either on a transient basis and/or a persistent basis.Further, a computer readable storage device does not include apropagation medium, such as a signal or carrier wave. Memory 106, inthis example, may be a main memory device, such as a dynamic randomaccess memory (DRAM), or any other suitable volatile or non-volatilestorage device, of data processing system 100.

Storage-class memory 108 may be, for example, a phase change memory(PCM) and/or a solid-state drive (SSD). A phase change memory is anon-volatile solid-state data storage memory device employing phasechange materials that change between two states, namely an amorphousstate and a poly-crystalline state. A solid-state drive uses integratedcircuit assemblies as memory to store data persistently. Storage-classmemory 108 uses electronic interfaces compatible with memory 106 andpersistent storage 110. Storage-class memory 108 has lower access timeand less latency than persistent storage 110.

In this example, storage-class memory 108 includes user-generateddatabase schema 120 and delta change data store 122. User-generateddatabase schema 120 is a structure for organizing stored data recordswithin a database and is created by a user of data processing system100. User-generated database schema 120 may be, for example, arelational database schema. However, it should be noted thatuser-generated database schema 120 may represent any type of schema,such as a row-based schema, a column-based schema, or any other schemaformat. Delta change data store 122 is a data storage area that storesrecent changes to data records, such as data records 126, within table124. The recent changes to data records may be, for example, insertionsof new data records, updates to data records, and/or deletions of datarecords. The data records may represent any type of recorded data. Forexample, the data records may be associated with a monitoringapplication that receives a multitude of readings at a very rapid pacefrom thousands of sensors. In other words, the stored data recordswithin delta change data store 122 may change often (i.e., updatedrapidly and frequently).

In addition, data records 126 include flags 128. Each data record indata records 126 has a corresponding flag. Flags 128 are delete flagsthat indicate whether a corresponding data record is to be deleted ornot. For example, a flag may be set to true, which indicates that acorresponding data record is to be deleted. Alternatively, a flag may beset to false, which indicates that the corresponding data record is notto be deleted. Flags 128 may be, for example, Boolean attributes addedto a data record. Alternatively, flags 128 may be bits added to a datarecord.

Persistent storage 110 may take various forms, depending on theparticular implementation. For example, persistent storage 110 maycontain one or more devices. For example, persistent storage 110 may bea magnetic hard disc drive (HDD), a flash memory, a rewritable opticaldisk, a rewritable magnetic tape drive, or some combination of theabove. The media used by persistent storage 110 may be removable. Forexample, a removable hard disc drive may be used for persistent storage110.

In this example, persistent storage 110 includes user-generated databaseschema 130 and stable data store 132. User-generated database schema 130is identical or substantially the same as user-generated database schema122. In other words, data processing system 100 applies the samedatabase schema to both delta change data store 122 and stable datastore 132.

Stable data store 132 is a data storage area that stores a plurality ofdata records, such as data records 136, within table 134. Data records136 represent previous versions of data records that are currentlystored on delta change data store 122 and/or data records that werepreviously stored on delta change data store 122. In other words, datarecords 136 represent data records that data processing system 100pushes from delta change data store 122 to stable data store 132 after,for example, a predetermined time interval expires, a number of datarecords stored within delta change data store 122 exceeds apredetermined threshold number of data records, or an occurrence of apredefined event.

Also in this example, persistent storage 110 stores pre-definedrelational algebra rules 138. Pre-defined relational algebra rules 138represent a plurality of relational algebra rules that were previouslydefined by the user of data processing system 100 to rewrite dataqueries received by data processing system 100. Pre-defined relationalalgebra rules 138 are rules for performing different types of data queryoperations, such as data record select, data record insert, data recordupdate, and data record delete operations. Data processing system 100utilizes a different relational algebra rule for each different dataquery operation.

Relational algebra is a formal description of how a relational databaseoperates. In other words, relational algebra is a mathematicalexpression that underpins standard query language (SQL) operations. Inorder to implement a database management system, a set of rules mustexist that state how a database is to operate. For example, when a userwants to insert a new data record within a table of the database, a setof rules must exist to ensure that the database management systeminserts the new data record as the user expects.

Communications unit 112, in this example, provides for communicationwith other data processing systems and computing devices. Communicationsunit 112 may provide communications through the use of either or bothphysical and wireless communications links. The physical communicationslink may utilize, for example, a wire, cable, universal serial bus, orany other physical technology to establish a physical communicationslink for data processing system 100. The wireless communications linkmay utilize, for example, shortwave, high frequency, ultra highfrequency, microwave, wireless fidelity (Wi-Fi), bluetooth technology,global system for mobile communications (GSM), code division multipleaccess (CDMA), second-generation (2G), third-generation (3G),fourth-generation (4G), or any other wireless communication technologyor standard to establish a wireless communications link for dataprocessing system 100.

Input/output unit 114 allows for the input and output of data with otherdevices that may be connected to data processing system 100. Forexample, input/output unit 114 may provide a connection for user inputthrough a keypad, a keyboard, a mouse, and/or some other suitable inputdevice. Display 116 provides a mechanism to display information to auser. In addition, display 116 may provide touch screen capabilities.

Instructions for the operating system, applications, and/or programs maybe located in storage devices 118, which are in communication withprocessor unit 104 through communications fabric 102. In thisillustrative example, the instructions are in a functional form onpersistent storage 110. These instructions may be loaded into memory 106for running by processor unit 104. The processes of the differentembodiments may be performed by processor unit 104 using computerimplemented instructions, which may be located in a main memory, such asmemory 106. These instructions are referred to as program code, computerusable program code, or computer readable program code that may be readand run by a processor in processor unit 104. The program code, in thedifferent embodiments, may be embodied on different physical computerreadable storage devices, such as memory 106, storage-class memory 108,or persistent storage 110.

Program code 140 is located in a functional form on computer readablemedia 142 that is selectively removable and may be loaded onto ortransferred to data processing system 100 for running by processor unit104. Program code 140 and computer readable media 142 form computerprogram product 144. In one example, computer readable media 142 may becomputer readable storage media 146 or computer readable signal media148. Computer readable storage media 146 may include, for example, anoptical or magnetic disc that is inserted or placed into a drive orother device that is part of persistent storage 110 for transfer onto astorage device, such as a magnetic hard disc drive, that is part ofpersistent storage 110. Computer readable storage media 146 also maytake the form of a persistent storage device, such as a hard drive, athumb drive, or a flash memory that is connected to data processingsystem 100. In some instances, computer readable storage media 146 maynot be removable from data processing system 100.

Alternatively, program code 140 may be transferred to data processingsystem 100 using computer readable signal media 148. Computer readablesignal media 148 may be, for example, a propagated data signalcontaining program code 140. For example, computer readable signal media148 may be an electro-magnetic signal, an optical signal, and/or anyother suitable type of signal. These signals may be transmitted overcommunication links, such as wireless communication links, an opticalfiber cable, a coaxial cable, a wire, and/or any other suitable type ofcommunications link. In other words, the communications link and/or theconnection may be physical or wireless in the illustrative examples. Thecomputer readable media also may take the form of non-tangible media,such as communication links or wireless transmissions containing theprogram code.

In some illustrative embodiments, program code 140 may be downloadedover a network to persistent storage 110 from another device or dataprocessing system through computer readable signal media 148 for usewithin data processing system 100. For instance, program code stored ina computer readable storage media in a server data processing system maybe downloaded over a network from the server to data processing system100. The data processing system providing program code 140 may be aserver computer, a client computer, or some other device capable ofstoring and transmitting program code 140.

The different components illustrated for data processing system 100 arenot meant to provide architectural limitations to the manner in whichdifferent embodiments may be implemented. The different illustrativeembodiments may be implemented in a data processing system includingcomponents in addition to, or in place of, those illustrated for dataprocessing system 100. Other components shown in FIG. 1 can be variedfrom the illustrative examples shown. The different embodiments may beimplemented using any hardware device or system capable of executingprogram code. As one example, data processing system 100 may includeorganic components integrated with inorganic components and/or may becomprised entirely of organic components excluding a human being. Forexample, a storage device may be comprised of an organic semiconductor.

As another example, a computer readable storage device in dataprocessing system 100 is any hardware apparatus that may store data.Memory 106, storage-class memory 108, persistent storage 110, andcomputer readable storage media 146 are examples of physical computerreadable storage devices in a tangible form.

In another example, a bus system may be used to implement communicationsfabric 102 and may be comprised of one or more buses, such as a systembus or an input/output bus. Of course, the bus system may be implementedusing any suitable type of architecture that provides for a transfer ofdata between different components or devices attached to the bus system.Additionally, a communications unit may include one or more devices usedto transmit and receive data, such as a modem or a network adapter.Further, a memory may be, for example, memory 106 or a cache such asfound in an interface and memory controller hub that may be present incommunications fabric 102.

In the course of developing illustrative embodiments, it was discoveredthat the overhead associated with changes to data records needs to bereduced so that indexes may be effectively used for analytical dataquery processing without being a heavy burden on transactional dataquery throughput. To address this need, illustrative embodiments utilizea solid-state storage device layer within a data storage hierarchy.Based on current technologies, solid-state drives are orders ofmagnitude faster than magnetic hard disk drives for small random dataaccess inputs/outputs. However, per gigabyte, solid-state disk drivesare more expensive than magnetic hard disk drives. As a result, it paysto store the bulk of data records on the magnetic hard disk drive andreserve the solid-state drive for data records that can benefit the mostfrom utilizing the faster storage medium, such as, for example, datarecords that are accessed frequently and randomly.

Unlike previous approaches, illustrative embodiments do not simply store“hot” data records on the solid-state drive. Instead, illustrativeembodiments utilize a query rewriting process to extend the data storagehierarchy by employing a data record staging area on the solid-statedrive to absorb the cost of data record update transactions and toperiodically batch these data record updates to the hard disk drive.Because the solid-state drive is a faster storage medium than the harddisk drive, illustrative embodiments are able to efficiently processthese transactions that change the data records. Using the queryrewriting process, illustrative embodiments decrease the number ofmagnetic hard disk drive input/outputs that are needed for updating thedata records and indexes. In addition, illustrative embodiments onlyrequire solid-state drive input/outputs for data record insertions,deletions, and updates. It should be noted that even though illustrativeembodiments are described in terms of utilizing a solid-state drive,illustrative embodiments are not limited to such. For example,alternative illustrative embodiments may utilize an auto-commit memory(ACM) with smaller input/output granularities that may provide evenbetter performance.

To support efficient data record changes by leveraging the presence of asolid-state drive as part of the data storage hierarchy, illustrativeembodiments defer the data record changes by only maintaining the recentdata record changes entirely on the solid-state drive while storing themore stable portion of the data records on the magnetic hard disk drive.This approach enables illustrative embodiments to efficiently storerecent data record updates on the solid-state drive and to onlyperiodically merge the data record content of the solid-state drive withthe data record content of the hard disk drive in batches, therebyamortizing disk update cost. Furthermore, illustrative embodiments aredeclaratively implemented through query rewriting without changing thedatabase program; thus, providing a cost-effective and non-intrusiveprocess for supporting faster data record updates.

Deferring data record updates is in contrast with static pre-allocationof database objects to either the solid-state drive or the hard diskdrive because illustrative embodiments utilize the deferred data recordupdates by dynamically allocating only recent data record changes to thesolid-state drive. This deferred data record update scheme ofillustrative embodiments also differs from extending the buffer poolsize for dynamically caching hot pages, in which solid-state drivebuffer pool pages are an identical copy of pages stored on the hard diskdrive. However, when illustrative embodiments defer data record updates,the data record content of the solid-state drive and the data recordcontent of the hard disk drive are strictly different.

The data query rewriting process of illustrative embodiments: 1)supports the complete class of transactional data query operations, suchas insert, update, and delete; 2) enables batching of data recordupdates and sequential writes by periodically pushing the stored datarecord updates on the solid-state drive to the hard disk drive; 3)exploits a full range of data access patterns, such as, for example,scan, hash-join, merge-join, and index lookup, as part of data queryoptimization; 4) eliminates the need to modify the database program,which is a non-intrusive approach; 5) utilizes the solid-state drive byproviding a faster storage medium for data record storage and lookupduring data queries and exploits both the fast random (index lookup) andsequential (table scan) read accesses; 6) extends the deferred datarecord updates to support a multi-version database by retaining all datarecord updates and deletes and by maintaining a secondary storagestructure on the solid-state drive to store the most recent version ofeach data record; and 7) employs a hybrid locking process that includes:a) a lock-free disk access, which does not lock individual data recordson the hard disk drive, but locks the entire table on the hard diskdrive when batching data record updates to the hard disk drive from thesolid-state drive; and b) traditional locking of individual data recordson solid-state drive when a user updates or deletes data records storedon the solid-state drive.

The deferred data record update scheme of illustrative embodiments alsomay be viewed as extending a database persistent storage hierarchy,which is conceptually similar to extending a buffer pool. In thisextended database persistent storage model, illustrative embodimentsstore and manage on the solid-state drive either the working set of datarecords (i.e., data records that are changed frequently) or the tail ofthe table. Illustrative embodiments implement this model either throughnon-materialized views (query rewriting) or through table partitioning(maintaining the latest active partition on the solid-state drive). Bothof these approaches provide consistent and transparent views of thedatabase to the user. Thus, illustrative embodiments hide the underlyingstorage model from both the user and the database program.

In addition, utilizing the query rewriting approach provides moreflexibility in terms of physical representation. For example,illustrative embodiments may store the updatable data records on thesolid-state drive as a row-based data structure representation and storethe data records on the hard disk drive as a column-based data structurerepresentation. Further, illustrative embodiments may transparentlyleverage other existing data structure representations, such as amulti-version or bi-temporal data structure representation.

Query rewriting for select, insert, update, and delete data queryoperations, which are expressed in relational algebra expressions,minimizes the number of hard disk drive input/output accesses. The queryrewriting of illustrative embodiments assumes roughly an identicaldatabase schema on both the hard disk drive and the solid-state drive.Illustrative embodiments define a relational database schema as a finiteset of tables. Each table contains a collection of columns. Illustrativeembodiments assume a single relation key for each column. If no explicitrelation key is defined, then the name of the column is the relationkey. Each column in a table has a unique name and is assigned a fixedposition in the table.

An instance over the relational database schema is a function thatassigns to each table a finite set of data records. Illustrativeembodiments define the relational database schema on the solid-statedrive such that for every table residing on the hard disk drive there iscorresponding table on the solid-state drive. When a data record on thesolid-state drive has a corresponding flag indicating that the datarecord should be deleted, then the data record must be removed from thetable on the hard disk drive if the data record exists on the hard diskdrive.

Thus, illustrative embodiments of the present invention provide acomputer-implemented method, computer system, and computer programproduct for staging data record changes from a faster storage medium toa slower storage medium using data query rewriting. In response to acomputer receiving a data query corresponding to a particular datarecord, the computer determines whether the data query is one of atransactional data query or an analytical data query. In response to thecomputer determining that the data query is a transactional data query,the computer rewrites the transactional data query to applytransactional delta changes to the particular data record on astorage-class memory of the computer. In response to the computerdetermining that the data query is an analytical data query, thecomputer rewrites the analytical data query to select and reconcile eachdata record corresponding to the particular data record stored on thestorage-class memory with the particular data record stored on apersistent data storage device of the computer.

With reference now to FIG. 2, a diagram illustrating deferred datarecord updates using query rewriting is depicted in accordance with anillustrative embodiment. Deferred updates using query rewriting 200 isimplemented in computer system 202. Computer system 202 may be, forexample, data processing system 100 in FIG. 1. Computer system 202includes record database 204, which is comprised of solid-state drive206 and hard disk drive 208. Solid-state drive 206 and hard disk drive208 may be, for example, storage-class memory 108 and persistent storage110 in FIG. 1, respectively.

Solid-state drive 206 includes delta change data store 210. Delta changedata store 210 may be, for example, delta change data store 122 inFIG. 1. Delta change data store 210 is a data storage area that storesrecent changes to data records, such as updates and deletes, and/orrecent data record inserts. Delta change data store 210 may store theupdates, deletes, and inserts of data records in a table, such as table124 in FIG. 1. Hard disk drive 208 includes stable data store 212.Stable data store 212 may be, for example, stable data store 132 inFIG. 1. Stable data store 212 is a data storage area that stores datarecords that computer system 202 pushes from delta change data store 210to stable data store 212 at the expiration of a predetermined timeinterval, when a number of data records stored within delta change datastore 122 exceeds a predetermined threshold number of data records, orwhen a predefined event occurs, for example. Stable data store 212 maystore the data records in a table, such as table 134 in FIG. 1.

Computer system 202 receives data queries, such as transactional dataquery 214 and analytical data query 216, to perform operations on datarecords within records database 204. Transactional data query 214 maybe, for example, an insert data query, an update data query, or a deletedata query. Analytical data query 216 may be, for example, a select dataquery.

Computer system 202 utilizes query rewriting process 218 to rewrite thereceived data queries. For example, computer system 202 utilizes queryrewriting process 218 to rewrite transactional data query 214 togenerate rewritten transactional data query 220. Similarly, computersystem 202 utilizes query rewriting process 218 to rewrite analyticaldata query 216 to generate rewritten analytical data query 222. Queryrewriting process 218 utilizes pre-defined relational algebra rules,such as pre-defined relational algebra rules 138 in FIG. 1, to generaterewritten transactional data query 220 and rewritten analytical dataquery 222.

Computer system 202 issues rewritten transactional data query 210 torecord database 204. However, it should be noted that query rewritingprocess 218 rewrites transactional data query 214 so that alltransactional data queries, such as inserts, updates, and deletes, areonly applied to delta change data store 210 on solid-state drive 206.Similarly, computer system 202 issues rewritten analytical data query222 to record database 204. It should be noted that query rewritingprocess 218 rewrites analytical data query 216 so that all analyticaldata queries, such as select data queries, are applied to both deltachange data store 210 on solid-state drive 206 and stable data store 212on hard disk drive 208 to reconcile different versions of data recordsassociated with a particular analytical data query.

With reference now to FIG. 3, a diagram illustrating an example ofreconciling data records during a select data query operation isdepicted in accordance with an illustrative embodiment. Reconciling datarecords during a select data query operation 300 may be implemented in acomputer, such as computer system 202 in FIG. 2. Reconciling datarecords during a select data query operation 300 utilizes hard diskdrive 302 and solid-state drive 304. Hard disk drive 302 may be, forexample, hard disk drive 208 in FIG. 2. Solid-state drive 304 may be,for example, solid-state drive 206 in FIG. 2.

In this example, hard disk drive 302 includes stable data store 306 andsolid-state drive 304 includes delta change data store 308. Stable datastore 306 and delta change data store 308 may be, for example, stabledata store 212 and delta change data store 210 in FIG. 2, respectively.However, it should be noted that illustrative embodiments are notrestricted to storing stable data store 306 on hard disk drive 302 andstoring delta change data store 308 on solid-state drive 304. Forexample, alternative illustrative embodiments may store stable datastore 306 on a different type of persistent data storage device, such asa magnetic tape drive. In addition, alternative illustrative embodimentsmay store delta change data store 308 on a different type ofstorage-class memory, such as a phase-change memory or an auto-commitmemory.

Also in this example, hard disk drive 302 stores data records 310, 312,314, and 316 within a table, such as table 134 in FIG. 1, in stable datastore 306. Solid-state drive 304 stores updates to data records 310 and316 within a table, such as table 124 in FIG. 1, in delta change datastore 308. In addition, solid-state drive 304 stores a deletion of datarecord 312. It should be noted that illustrative embodiments extendsolid-state drive 304 to include flags, such as delete flags 318, 320,and 322. Also, it should be noted that each flag corresponds to aparticular data record. For example, delete flag 318 corresponds to datarecord 310, delete flag 320 corresponds to data record 312, and deleteflag 322 corresponds to data record 316. Further, it should be notedthat delete flag 318 corresponding to data record 310 is set to false(F), delete flag 320 corresponding to data record 312 is set to true(T), and delete flag 322 corresponding to data record 316 is set tofalse. In other words, delete flag 320, which is set to true, indicatesthat data record 312 is to be deleted or removed. Delete flags 318 and322, which are set to false, indicate that data records 310 and 316 arenot to be deleted or removed.

In this example assume that the computer received a data query toperform a select data query operation on data records 310-316. Thecomputer rewrites the select data query using a predefined relationalalgebra rule that corresponds to the select data query. The rewrittenselect data query reconciles the data records stored on hard disk drive302 with the data record changes stored on solid-state drive 304 basedon each data record's corresponding delete flag setting. For example, inthis illustration the computer reconciles data records 310 and 316 withthe changes stored in delta change data store 308 and removes datarecord 312 because corresponding delete flag 320 is set to true. As aresult, rewritten data query result 324 includes data record 314 andupdated data records 310 and 316, but not removed data record 312.Rewritten data query result 324 may be, for example, a non-materializedview. A non-materialized view is a logical table-like structurepopulated on the fly by a given data query. The non-materialized viewresults of the given data query are not stored anywhere on disk and thenon-materialized view is recreated every time the query is executed.Conversely, materialized views are actual data structures that arestored on disk.

Illustrative embodiments focus on rewriting the access to the table onstable data store 306 for a particular select data query byconsolidating both the table on stable data store 306 and itscorresponding deferred data update table on delta change data store 308.This merging of data record content of the table on stable data store306 with its more recent data record updates stored on the deferred dataupdate table on delta change data store 308 can be expressed in arelational algebra rewriting as for example:R

(R−π _(R)(R′))∪π_(R)(σ_(isDeleted=False)(R′)).

One subtlety in the above relational algebra rewriting rule is that thecomputer eliminates all data records that are to be deleted from stabledata store 306. In other words, the computer only includes those datarecords within rewritten data query result 324 that have theircorresponding delete flag set to false in delta change data store 308.Data query rewriting also is associative and composable with respect toother relational algebra operators, such as selection. Hence, data queryrewriting forms the building block for mapping complex data queries thatalso may directly benefit from data query optimization, such aspushing-down the data record selections to stable data store 306.

With reference now to FIG. 4, a diagram illustrating an example ofreconciling data records during an insert data query operation isdepicted in accordance with an illustrative embodiment. Reconciling datarecords during an insert data query operation 400 may be implemented ina computer, such as computer system 202 in FIG. 2. Reconciling datarecords during an insert data query operation 400 utilizes hard diskdrive 402 and solid-state drive 404. Hard disk drive 402 may be, forexample, hard disk drive 208 in FIG. 2. Solid-state drive 404 may be,for example, solid-state drive 206 in FIG. 2.

In this example, hard disk drive 402 includes stable data store 406 andsolid-state drive 404 includes delta change data store 408. Stable datastore 406 and delta change data store 408 may be, for example, stabledata store 212 and delta change data store 210 in FIG. 2, respectively.Also in this example, hard disk drive 402 stores data records 410, 412,414, and 416 within a table, such as table 134 in FIG. 1, in stable datastore 406. Solid-state drive 404 stores an update to data record 410within a table, such as table 124 in FIG. 1, in delta change data store408.

In this example assume that the computer received a data query toperform an insert data query operation on data record inserts 420. Datarecord inserts 420 include insertions of new data records 422 and 424.The computer rewrites the insert data query using a predefinedrelational algebra rule that corresponds to the insert data query, suchas, for example:R←R∪I

R′←R′∪π _(R,isDeleted=False)(I)−(I

R).

The rewritten insert data query performs an insert operation for datarecords 422 and 424 on solid-state drive 404. As a result, solid-statedrive 404 now includes updated data record 410 and newly inserted datarecords 422 and 424. It should be noted that delete flag 418 correspondsto updated data record 410, delete flag 426 corresponds to inserted datarecord 422, and delete flag 428 corresponds to inserted data record 424.Also, it should be noted that delete flags 418, 426, and 428 are set tofalse. In other words, delete flags 418, 426, and 428, which are set tofalse, indicate that corresponding data records 410, 422, and 424 arenot to be deleted or removed.

Illustrative embodiments define the insert data query as simply adding anew set of one or more data records to an existing table. Since the setof data records to be inserted (e.g., data record inserts 420) is themost recent changes to the database, then illustrative embodiments addthe set of data records to the table on solid-state drive 404 as opposedto the table on hard disk drive 402. In addition, illustrativeembodiments set the delete flag corresponding to these newly inserteddata records to false. Further, if any unique constraint exists on thetable of hard disk drive 402, then illustrative embodiments also satisfythis constraint by removing any new data record in data record inserts420 that already exists in the table.

With reference now to FIG. 5, a diagram illustrating an example ofreconciling data records during a delete data query operation isdepicted in accordance with an illustrative embodiment. Reconciling datarecords during a delete data query operation 500 may be implemented in acomputer, such as computer system 202 in FIG. 2. Reconciling datarecords during a delete data query operation 500 utilizes hard diskdrive 502 and solid-state drive 504. Hard disk drive 502 may be, forexample, hard disk drive 208 in FIG. 2. Solid-state drive 504 may be,for example, solid-state drive 206 in FIG. 2.

In this example, hard disk drive 502 includes stable data store 506 andsolid-state drive 504 includes delta change data store 508. Stable datastore 506 and delta change data store 508 may be, for example, stabledata store 212 and delta change data store 210 in FIG. 2, respectively.Also in this example, hard disk drive 502 stores data records 510, 512,514, and 516 within a table, such as table 134 in FIG. 1, in stable datastore 506. Solid-state drive 504 stores an update to data record 510 andrecently inserted data record 518 within a table, such as table 124 inFIG. 1, in delta change data store 508. Delete flags 520 and 522corresponding to data records 510 and 518, respectively, are set tofalse.

In this example assume that the computer received a data query toperform a delete data query operation on data record deletes 524. Datarecord deletes 524 include deletions of data records 512 and 518. Thecomputer rewrites the delete data query using a predefined relationalalgebra rule that corresponds to the delete data query, such as, forexample:R←R−D

R′←(R′∪π _(R,isDeleted=True)(D))−D

R).

The rewritten delete data query performs a delete operation on datarecord 512 on hard disk drive 502 and on data record 518 on solid-statedrive 504. As a result of the delete operation, data record 518 isremoved from solid-state drive 504. In other words, the computer neverpushed recently inserted data record 518 to hard disk drive 502 and,therefore, removed it from solid-state drive 504. In addition,solid-state drive 504 now includes updated data record 510 and deleteddata record 512. It should be noted that delete flag 526 correspondingto deleted data record 512 is set to true. In other words, delete flag526 indicates that corresponding data record 512 is to be deleted orremoved from hard disk drive 502 when the computer determines that it istime to push data records from solid-state drive 504 to hard disk drive502.

The delete data query is similar to the insert data query except thatillustrative embodiments tag the removed set of data records associatedwith the delete data query as deleted in solid-state drive 504. In otherwords, illustrative embodiments set corresponding delete flags of theremoved set of data records to true. It should be noted that deleteddata records should actually exist in the table of hard disk drive 502.Illustrative embodiments achieve this delete operation by performing ananti join operation on hard disk drive 502. Verifying the existence ofremoved data records is an optimization, which is not necessary forproving the correctness of a delete operation.

With reference now to FIG. 6, a diagram illustrating an example ofreconciling data records during an update data query operation isdepicted in accordance with an illustrative embodiment. Reconciling datarecords during an update data query operation 600 may be implemented ina computer, such as computer system 202 in FIG. 2. Reconciling datarecords during an update data query operation 600 utilizes hard diskdrive 602 and solid-state drive 604. Hard disk drive 602 may be, forexample, hard disk drive 208 in FIG. 2. Solid-state drive 604 may be,for example, solid-state drive 206 in FIG. 2.

In this example, hard disk drive 602 includes stable data store 606 andsolid-state drive 604 includes delta change data store 608. Stable datastore 606 and delta change data store 608 may be, for example, stabledata store 212 and delta change data store 210 in FIG. 2, respectively.Also in this example, hard disk drive 602 stores data records 610, 612,614, and 616 within a table, such as table 134 in FIG. 1, in stable datastore 606. Solid-state drive 604 stores a recent update to data record610 within a table, such as table 124 in FIG. 1, in delta change datastore 608. Delete flag 618 corresponding to data record 610 is set tofalse.

In this example assume that the computer received a data query toperform an update data query operation on data record updates 620. Datarecord updates 620 include an update to recently updated data record 610and an update to data record 616. The computer rewrites the update dataquery using a predefined relational algebra rule that corresponds to theupdate data query, such as, for example:R←R∪U

R′←((R′−π _(R,isDeleted=False)(U))∪π_(R,isDeleted=False)(U)).

The rewritten update data query performs an update operation on recentlyupdated data record 610 and on data record 616. As a result of theupdate operation, solid-state drive 604 now includes updated datarecords 610 and 616. It should be noted that the computer removes theprevious update to data record 610 and replaces it with the new orcurrent update. Also, it should be noted that delete flag 622corresponding to recently updated data record 616 is set to false. Inother words, delete flag 622 indicates that corresponding data record616 is not to be deleted or removed.

In order to capture the updated set of data records for the table onsolid-state drive 604, assuming only the most recent version of eachdata record is stored on solid-state drive 604, the computer firstremoves any previous data record update entries associated with the setof updated data record from solid-state drive 604 followed by adding thenew set of updated data record to solid-state drive 604. The computermay process the rewritten update data query in two steps, for example.In order to retain a complete history of each data record, the computerdrops the first portion of the above predefined relational algebrarewriting rule and adds a set of additional attributes for tracking thedifferent versions of a data record.

With reference now to FIG. 7, a flowchart illustrating a process forgenerating a database to store data records is shown in accordance withan illustrative embodiment. The process shown in FIG. 7 may beimplemented in a computer, such as, for example, data processing system100 in FIG. 1.

The process begins when the computer receives a user-generated databaseschema associated with a table of data records, such as, for example,user-generated database schema 120 associated with table 124 of datarecords 126 in FIG. 1 (step 702). After receiving the user-generateddatabase schema in step 702, the computer applies the user-generateddatabase schema associated with the table of data records to a stabledata store on a hard disk drive of the computer, such as, for example,stable data store 132 on persistent storage 100 in FIG. 1 (step 704). Inaddition, the computer applies the user-generated database schemaassociated with the table of data records to a delta change data storeon a solid-state drive of the computer, such as, for example, deltachange data store 122 on storage-class memory 108 in FIG. 1 (step 706).Further, the computer extends the user-generated database schemaassociated with the table of data records on the delta change data storeto include a flag for each data record in the table of data records,such as for example, delete flags 318-322 in FIG. 3, indicating whethera particular data record is to be deleted or not (step 708). Thereafter,the process terminates.

With reference now to FIG. 8, a flowchart illustrating a process forrewriting data queries is shown in accordance with an illustrativeembodiment. The process shown in FIG. 8 may be implemented in acomputer, such as, for example, data processing system 100 in FIG. 1.

The process begins when the computer receives a data query, such astransactional data query 214 or analytical data query 216 in FIG. 2,corresponding to a particular data record (step 802). After receivingthe data query in step 802, the computer makes a determination as towhether the data query is a transactional data query (step 804). If thecomputer determines that the data query is a transactional data query,yes output of step 804, then the computer rewrites the transactionaldata query to only apply transactional delta changes to the particulardata record on a storage-class memory device of the computer, such assolid-state drive 206 of computer system 202 in FIG. 2 (step 806).Thereafter, the process terminates. If the computer determines that thedata query is an analytical data query, no output of step 804, then thecomputer rewrites the analytical data query to select and reconcile eachdata record corresponding to the particular data record stored on thestorage-class memory device with the particular data record stored on apersistent data storage device of the computer, such as hard disk drive208 of computer system 202 in FIG. 2 (step 808). Thereafter, the processterminates.

With reference now to FIG. 9, a flowchart illustrating a process forquerying a database is shown in accordance with an illustrativeembodiment. The process shown in FIG. 9 may be implemented in acomputer, such as, for example, data processing system 100 in FIG. 1.

The process begins when the computer receives a data query, such astransactional data query 214 or analytical data query 216 in FIG. 2, toperform a particular operation on a set of one or more data recordswithin a table of data records that is based on a user-generateddatabase schema (step 902). The set of data records within the table ofdata records based on the user-generated database schema may be, forexample, one or more of data records 126 within table 124, which isbased on user-generated database schema 120 in FIG. 2. After receivingthe data query in step 902, the computer rewrites the data query using,for example, query rewriting process 218 in FIG. 2, based on apre-defined relational algebra rule associated with the particularoperation to reflect that stable data records are stored on a hard diskdrive of the computer and that recent delta changes to data records arestored on a solid-state drive of the computer (step 904). Thepre-defined relational algebra rule may be, for example, one rule inpre-defined relational algebra rules 138 in FIG. 1. The hard disk driveand solid-state drive of the computer may be, for example, hard diskdrive 208 and solid-state drive 206 of computer system 202 in FIG. 2.

Subsequent to rewriting the data query in step 904, the computer issuesthe rewritten data query based on the pre-defined relational algebrarule associated with the particular operation to a stable data store onthe hard disk drive of the computer (step 906). For example, computersystem 202 issues rewritten analytical data query 222 to stable datastore 212 in FIG. 2. In addition, the computer issues the rewritten dataquery based on the pre-defined relational algebra rule associated withthe particular operation to a delta change data store, such as deltachange data store 210 in FIG. 2, on the solid-state drive of thecomputer (step 908). Thereafter, the process terminates.

With reference now to FIG. 10, a flowchart illustrating a process forperforming a select data query is shown in accordance with anillustrative embodiment. The process shown in FIG. 10 may be implementedin a computer, such as, for example, data processing system 100 in FIG.1.

The process begins when the computer receives a select data query toperform a select data record operation on a set of data records within atable of data records that is based on a user-generated database schema(step 1002). Afterward, the computer rewrites the select data querybased on a pre-defined relational algebra rule associated with theselect data record operation (step 1004). Subsequently, the computerexecutes the rewritten select data query based on the pre-definedrelational algebra rule associated with the select data record operationon a stable data store on a hard disk drive of the computer (step 1006).In addition, the computer executes the re-written select data querybased on the pre-defined relational algebra rule associated with theselect data record operation on a delta change data store on asolid-state drive of the computer (step 1008).

Then, the computer removes each data record that appears in a selectquery result of the delta change data store on the solid-state drivefrom a select query result of the stable data store on the hard diskdrive to generate a stable data store select query result correspondingto the set of data records (step 1010). Further, the computer removeseach data record that includes a delete flag set to true from the queryresult of the delta change data store on the solid-state drive togenerate a delta change data store select query result corresponding tothe set of data records (step 1012). Furthermore, the computer combinesthe stable data store select query result with the delta change datastore query result to generate a final select query result correspondingto the set of data records, such as rewritten data query result 324 inFIG. 3 (step 1014). Then, the computer outputs the final select queryresult corresponding to the set of data records as a non-materializedview (step 1016). Thereafter, the process terminates.

With reference now to FIG. 11, a flowchart illustrating a process forperforming an insert data query is shown in accordance with anillustrative embodiment. The process shown in FIG. 11 may be implementedin a computer, such as, for example, data processing system 100 in FIG.1.

The process begins when the computer an insert data query to perform aninsert data record operation on a data record (step 1102). Afterward,the computer rewrites the insert data query based on a pre-definedrelational algebra rule associated with the insert data record operation(step 1104). Further, the computer makes a determination as to whetherthe data record to be inserted exists within a table of data records oneither a stable data store on a hard disk drive of the computer or adelta change data store on a solid-state drive of the computer (step1106).

If the computer determines that the data record to be inserted doesexist within a table of data records on either a stable data store on ahard disk drive of the computer or a delta change data store on asolid-state drive of the computer, yes output of step 1106, then theprocess terminates thereafter. If the computer determines that the datarecord to be inserted does not exist within a table of data records oneither a stable data store on a hard disk drive of the computer or adelta change data store on a solid-state drive of the computer, nooutput of step 1106, then the computer inserts the data record into thetable of data records on the delta change data store on the solid-statedrive using the rewritten insert data query (step 1108). In addition,the computer sets a delete flag associated with the inserted data recordto false, such as delete flag 418 in FIG. 4 (step 1110). Thereafter, theprocess terminates.

With reference now to FIG. 12, a flowchart illustrating a process forperforming an update data query is shown in accordance with anillustrative embodiment. The process shown in FIG. 12 may be implementedin a computer, such as, for example, data processing system 100 in FIG.1.

The process begins when the computer receives an update data query toperform an update data record operation on a data record (step 1202).Afterward, the computer rewrites the update data query based on apre-defined relational algebra rule associated with the update datarecord operation (step 1204). Further, the computer makes adetermination as to whether the data record to be updated exists withina table of data records on a delta change data store on a solid-statedrive of the computer (step 1206).

If the computer determines that the data record to be updated does notexist within a table of data records on the delta change data store onthe solid-state drive of the computer, no output of step 1206, then theprocess proceeds to step 1210. If the computer determines that the datarecord to be updated does exist within a table of data records on thedelta change data store on the solid-state drive of the computer, yesoutput of step 1206, then the computer removes previous updates to thedata record from the table of data records on the delta change datastore on the solid-state drive using the re-written update data query(step 1208). In addition, the computer adds new updates to the datarecord to the table of data records on the delta change data store onthe solid-state drive using the re-written update data query (step1210). Thereafter, the process terminates.

With reference now to FIG. 13, a flowchart illustrating a process forperforming a delete data query is shown in accordance with anillustrative embodiment. The process shown in FIG. 13 may be implementedin a computer, such as, for example, data processing system 100 in FIG.1.

The process begins when the computer receives a delete data query toperform a delete data record operation on a data record (step 1302).Afterward, the computer rewrites the delete data query based on apre-defined relational algebra rule associated with the delete datarecord operation (step 1304). Further, the computer makes adetermination as to whether the data record to be deleted exists withina table of data records on a stable data store on a hard disk drive ofthe computer (step 1306).

If the computer determines that the data record to be deleted does notexist within a table of data records on the stable data store on thehard disk drive of the computer, no output of step 1306, then thecomputer makes a determination as to whether the data record to bedeleted exists within a table of data records on a delta change datastore on a solid-state drive of the computer (step 1308). If thecomputer determines that the data record to be deleted does not existwithin a table of data records on the delta change data store on thesolid-state drive of the computer, no output of step 1308, then theprocess terminates thereafter. If the computer determines that the datarecord to be deleted does exist within a table of data records on thedelta change data store on the solid-state drive of the computer, yesoutput of step 1308, then the computer deletes the data record to bedeleted from the table of data records on the delta change data store onthe solid-state drive (step 1310). Thereafter, the process terminates.

Returning again to step 1306, if the computer determines that the datarecord to be deleted does exist within a table of data records on thestable data store on the hard disk drive of the computer, yes output ofstep 1306, then the computer makes a determination as to whether thedata record to be deleted exists within a table of data records on thedelta change data store on the solid-state drive of the computer (step1312). If the computer determines that the data record to be deleteddoes exist within a table of data records on the delta change data storeon the solid-state drive of the computer, yes output of step 1312, thenthe process proceeds to step 1316. If the computer determines that thedata record to be deleted does not exist within a table of data recordson the delta change data store on the solid-state drive of the computer,no output of step 1312, then the computer adds the data record to bedeleted to the table of data records on the delta change data store onthe solid-state drive (step 1314). In addition, the computer sets adelete flag associated with the data record to be deleted to true, suchas delete flag 526 in FIG. 5 (step 1316). Thereafter, the processterminates.

Thus, illustrative embodiments provide a computer-implemented method,computer program product, and computer system for staging data recordchanges from a faster storage medium to a slower storage medium usingdata query rewriting. The descriptions of the various illustrativeembodiments have been presented for purposes of illustration, but arenot intended to be exhaustive or limited to the embodiments disclosed.Many modifications and variations will be apparent to those of ordinaryskill in the art without departing from the scope and spirit of thedescribed embodiment. The terminology used herein was chosen to bestexplain the principles of the embodiment, the practical application ortechnical improvement over technologies found in the marketplace, or toenable others of ordinary skill in the art to understand the embodimentsdisclosed here.

The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof computer systems, computer implemented methods, and computer programproducts according to various illustrative embodiments. In this regard,each block in the flowchart or block diagrams may represent a module,segment, or portion of code, which comprises one or more executableinstructions for implementing the specified logical function(s). Itshould also be noted that, in some alternative implementations, thefunctions noted in the block may occur out of the order noted in thefigures. For example, two blocks shown in succession may, in fact, beexecuted substantially concurrently, or the blocks may sometimes beexecuted in the reverse order, depending upon the functionalityinvolved. It will also be noted that each block of the block diagramsand/or flowchart illustration, and combinations of blocks in the blockdiagrams and/or flowchart illustration, can be implemented by specialpurpose hardware-based systems that perform the specified functions oracts, or combinations of special purpose hardware and computerinstructions.

What is claimed is:
 1. A computer-implemented method for staging datarecord changes from a faster storage medium to a slower storage mediumusing data query rewriting, the computer-implemented method comprising:responsive to a computer receiving a data query corresponding to performa particular operation on a particular data record, rewriting, by thecomputer, the data query based on a pre-defined relational algebra ruleassociated with the particular operation to reflect that stable datarecords are stored on a hard disk drive of the computer and that recentchanges to data records are stored on a solid-state drive of thecomputer, wherein the pre-defined relational algebra rule associatedwith the particular operation is one of a plurality of differentpre-defined relational algebra rules, and wherein each different one ofthe plurality of different pre-defined relational algebra rules isassociated with a different corresponding data query operation in aplurality of data query operations; and issuing, by the computer, thedata query based on the pre-defined relational algebra rule associatedwith the particular operation to a stable data store on the hard diskdrive of the computer and to a delta change data store on thesolid-state drive of the computer; wherein data record changes aredeferred by storing recent data record changes entirely on thesolid-state drive and only periodically merging a first data recordcontent of the solid-state drive with a second data record content ofthe hard disk drive in batches; and wherein the plurality of differentpre-defined relational algebra rules are selected from a groupconsisting of:R

(R−π _(R)(R′))∪π_(R)(σ_(isDeleted=False)(R′)),R←R∪I

R′←R′∪π _(R,isDeleted=False)(I)−(I

R),R←R−D

R′←(R′∪π _(R,isDeleted=True)(D))−D

R) andR←R∪U

R′←((R′−π _(R,isDeleted=False)(U)).
 2. The computer-implemented methodof claim 1, further comprising: responsive to the computer receiving auser-generated database schema associated with database records,applying, by the computer, the user-generated database schema to thestable data store on the hard disk drive of the computer and to thedelta change data store on the solid-state drive of the computer,wherein the user-generated database schema is identical on both thestable data store of the hard disk drive and the delta change data storeof the solid-state drive.
 3. The computer-implemented method of claim 2,further comprising: extending, by the computer, the user-generateddatabase schema applied to the delta change data store on thesolid-state drive of the computer to include a flag for each data recordstored in the delta change data store indicating whether one or moredata records are to be deleted.
 4. The computer-implemented method ofclaim 1, further comprising: responsive to the computer receiving aselect data query to perform a select data record operation on a set ofdata records, rewriting, by the computer, the select data query based ona pre-defined relational algebra rule of the plurality of differentpre-defined relational algebra rules that is associated with the selectdata record operation; executing, by the computer, the select data querybased on the pre-defined relational algebra rule associated with theselect data record operation on the stable data store on the hard diskdrive of the computer and on the delta change data store on thesolid-state drive of the computer; removing, by the computer, each datarecord that appears in a first select query result of the delta changedata store on the solid-state drive from a second select query result ofthe stable data store on the hard disk drive to generate a stable datastore select query result corresponding to the set of data records;removing, by the computer, each data record that includes a delete flagset to true from the query result of the delta change data store on thesolid-state drive to generate a delta change data store select queryresult corresponding to the set of data records; and combining, by thecomputer, the stable data store select query result with the deltachange data store query result to generate a final select query resultcorresponding to the set of data records.
 5. The computer-implementedmethod of claim 1, further comprising: responsive to the computerreceiving an insert data query to perform an insert data recordoperation on a data record, rewriting, by the computer, the insert dataquery based on a pre-defined relational algebra rule of the plurality ofdifferent pre-defined relational algebra rules that is associated withthe insert data record operation; responsive to the computer determiningthat the data record to be inserted does not exist on at least one ofthe stable data store on the hard disk drive of the computer or thedelta change data store on the solid-state drive of the computer,inserting, by the computer, the data record into the delta change datastore on the solid-state drive using the insert data query; and setting,by the computer, a delete flag associated with the inserted data recordto false on the solid-state drive of the computer.
 6. Thecomputer-implemented method of claim 1, further comprising: responsiveto the computer receiving an update data query to perform an update datarecord operation on a data record, rewriting, by the computer, theupdate data query based on a pre-defined relational algebra rule of theplurality of different pre-defined relational algebra rules that isassociated with the update data record operation; responsive to thecomputer determining that the data record to be updated does existon-the delta change data store on the solid-state drive of the computer,removing, by the computer, previous updates to the data record on thedelta change data store on the solid-state drive using the update dataquery; and adding, by the computer, new updates to the data record tothe delta change data store on the solid-state drive using the updatedata query.
 7. The computer-implemented method of claim 1, furthercomprising: responsive to the computer receiving a delete data query toperform a delete data record operation on a data record, rewriting, bythe computer, the delete data query based on a pre-defined relationalalgebra rule of the plurality of different pre-defined relationalalgebra rules that is associated with the delete data record operation;responsive to the computer determining that the data record to bedeleted does not exist on the stable data store on the hard disk driveof the computer, determining, by the computer, whether the data recordto be deleted exists on the delta change data store on the solid-statedrive of the computer; and responsive to the computer determining thatthe data record to be deleted does exist on the delta change data storeon the solid-state drive, deleting, by the computer, the data record tobe deleted from the delta change data store on the solid-state drive. 8.The computer-implemented method of claim 7, further comprising:responsive to the computer determining that the data record to bedeleted does exist on the stable data store on the hard disk drive ofthe computer, determining, by the computer, whether the data record tobe deleted exists on the delta change data store on the solid-statedrive of the computer; responsive to the computer determining that thedata record to be deleted does not exist on the delta change data storeon the solid-state drive, adding, by the computer, the data record to bedeleted to the delta change data store on the solid-state drive of thecomputer; and setting, by the computer, a delete flag associated withthe data record to be deleted to true on the solid-state drive of thecomputer.
 9. The computer-implemented method of claim 1, wherein datarecord changes are staged from a fast storage medium to a slow storagemedium using data query rewriting so that in response to the computerreceiving a data query corresponding to a particular data record, thecomputer determines whether the data query is one of a transactionaldata query or an analytical data query and in response to the computerdetermining that the data query is a transactional data query, thecomputer rewrites the transactional data query to apply transactionaldelta changes to the particular data record on a storage-class memoryand in response to the computer determining that the data query is ananalytical data query, the computer rewrites the analytical data queryto select and reconcile each data record corresponding to the particulardata record stored on the storage-class memory with the particular datarecord stored on a persistent data storage device of the computer. 10.The computer-implemented method of claim 1, wherein when the data recordchanges are deferred, first data record content of the solid-state driveand second data record content of the hard disk drive are strictlydifferent and wherein query rewriting for select query operationsexpressed in relational algebra expressions minimizes a number of harddisk drive input/output accesses.
 11. The computer-implemented method ofclaim 1, wherein a relational database schema on the solid state driveis defined such that for every table residing on the hard disk drivethere is a corresponding table on the solid state drive; and whereinwhen a data record on the solid-state drive has a corresponding flagindicating that the data record should be deleted, then the data recordmust be removed from the table on the hard disk drive if the data recordexists on the hard disk drive.